A Power Assignment Mechanism for DS UWB Wireless Telemedicine System … · 2008-08-15 · Figure 1. The proposed DS UWB wireless indoor telemedicine system with power assignment

A Power Assignment Mechanism for DS UWB Wireless TelemedicineSystem with Unequal Error Protection

Chin-Feng Lin and Ching Yi-LiDepartment of Electrical Engineering

National Taiwan Ocean UniversityNo.2 Beinging Road, Keelung

Taiwan

invited paper by Prof. Nikos E. Mastorakis and Dr. T. Mihail

Abstract: - In this paper, we propose a power assignment mechanism for direct-sequence ultra-wideband (DSUWB) wireless telemedicine system with unequal error protection. An essential feature of this system is that itoffers larger power and schemes providing significant error protection for the transmission of medicalinformation that requires higher quality of service (QoS). To realize maximum resource utilization, or minimumtotal transmission power, we also include an M-ary binary offset keying (MBOK) strategy into the system. Thus,in the proposed medical system, high power, a long length MBOK code, and scheme providing significant errorprotection schemes are employed for the transmission of medical messages that require a stringent bit-error rate(BER). In contrast, low power, short length MBOK codes, and less capable error protection schemes areprovided for messages that can tolerate a high BER. A simulation is carried out to verify the proper functioningof the proposed system in a practical wireless telemedicine scenario.

Key-Words: - Wireless Telemedicine system, power assignment mechanism, DS-UWB, QoS, medical messages,unequal error protection.

1 IntroductionTelemedicine performed by employing a high-speedand robust advanced wireless communication system,such as the Home Tele-Care System can provideubiquitous emergent or health-monitoring medicalservices at any time [1-10]. The performance of amobile telemedicine system that adopts multi-codecode division multiple access (CDMA), or widebandCDMA, or orthogonal frequency divisionmultiplexing (OFDM), or direct-sequenceultra-wideband (DS UWB) techniques has beenscrupulously studied in our earlier work [2-6]. In [5],we discuss a power control scheme in an equal errorprotection DS UWB wireless telemedicine system. In[6], we discuss a DS UWB medical system. In thisstudy, we extend our previous research [5-6] byconsidering the use of power assignment schemesand M-ary binary offset keying (MBOK) codingstrategies in a DS UWB wireless telemedicine systemwith unequal error protection. In addition, we discussthe relation between the power weighting factor andpower saving.

Ultra-wideband technology is a new technologyfor short-range high-speed wireless multimediacommunication systems. The specificationscorresponding to a data rate of 1320 Mbps and

transmission range of 10 meters indicate that DSUWB is a suitable candidate with which transmissionplatforms for a wireless indoor telemedicine systemcan be developed. A generic definition used in theFCC’s First Report [11], which is also widelyaccepted by the industry, defines a UWB device asany device that can emit signals with a fractionalbandwidth greater than 0.2 or a bandwidth of at least500 MHz at all times. A DS UWB system can operatein two modes, at a transmission bandwidth of1.368GHz in a 4-GHz low central frequency bandand at a transmission bandwidth of 2.763GHz in an8.2-GHz high central frequency band. There are twokinds of multiple access techniques specified in theUWB standard, OFDM and the direct-sequence codedivision multiple access (DS-CDMA) UWBtechnique [8]. Several MBOK short spreading codescan be selected when employing DS UWB so thatvarious transmission rates can be supported. Forinstance, in low operating band operation, the use ofMBOK code lengths of 24, 12, 6, and 3 can result intransmission bit rates of 28Mbps, 55Mbps, 110 Mbps,and 220 Mbps, respectively. Short MBOK codes witha smaller spreading factor are suitable for high-ratetransmissions that require low capability for

12th WSEAS International Conference on SYSTEMS, Heraklion, Greece, July 22-24, 2008

ISBN: 978-960-6766-83-1 284 ISSN: 1790-2769

Figure 1. The proposed DS UWB wireless indoor telemedicine system with power assignment mechanism.

combating channel fading. Moreover, differentconvolution codes, K=6, coding rate=1/2, 2/3 and 3/4can be used based on channel conditions. K is theconstraint length for convolution code. For theproposed medical system, we employ a strategyinvolving high power, and a long length spreadingcodes strategy, and schemes offering significant errorprotection for the transmission of medical messagesthat require a stringent bit-error rate (BER). Incontrast, low power, short length spreading codes,and less capable error protection schemes areprovided for messages that can tolerate a high BER.This system can not only satisfies the quality ofservice (QoS) required by a telemedicine system, butalso maximizes the transmission bit rate or minimizesthe transmission power.

2 A Power Assignment Mechanism forDS UWB Wireless TelemedicineSystem

A sketch of the proposed DS UWB transportarchitecture for the wireless indoor telemedicinesystem is depicted in Figure 1. From this figure wecan observe that the wireless indoor telemedicinesystem under consideration can deal with varioustypes of signals such as (i) blood pressure and bodytemperature measured with a few bits, (ii) medicalinformation recorded by the electrocardiogram (ECG)device and electroencephalography (EEG) devices,(iii) mobile patients' history, and (iv) G.729 audiosignals and MPEG-4 CCD sensor video signals. Theprocessing of pre-recorded medical informationrequires the synchronous playback of time-dependentmedical data based on some pre-specified temporalrelations. For this purpose, a model with which

temporal constraints among various data objectsobservable at the time of playback can be specified isneeded for a patient. In this regard, a well-knownmodel, which is called the Object Composition PetriNet (OCPN) model, was presented in [14]. Animportant feature of the OCPN model is that temporalrelationships among the various components of amedical document including the types, sizes,throughput requirements, and the duration of theirpresence, can be illustrated. Based on the OCPNmodel, the blood pressure, body temperature, ECGand EEG signals of every patient are directlyconverted to data bit streams. However, audio signalsobtained from microphones and CCD sensor videosignals should be transformed before being used bythe model. In other words, the blood pressure, bodytemperature, the 108-kbps bit streams for 12-channelECG signals and the 262.114-kbps bit streams for 64-channel EEG signals of every patient are directlyconverted to data bit streams. However, a G.729encoder should be employed to compress the 64-kbpsaudio signals to 8-kbps audio bit streams, an MPEG-4encoder is adopted to convert the 147.456-Mbpsvideo signals into 15-Mbps video bit streams, and theJPEG2000 is used to compress the 3640-kbits X-raymedical image signal to form a 128-kbits image bitstream. In our transport architecture, the data, audio,and video bit streams compose data, audio, and videopackets, respectively. Since the OCPN model canspecify the throughput resulting from thetransmission of concurrent multimedia objects, thesum of the data, audio, and video packets can becalculated. Usually, in a wireless medical system , theQoS is different for various messages. Here, weassume that the acceptable BERs for data, audio, andvideo packets are 710 , 310 , and 410 , respectively[7]. For this purpose, it is assumed that the system canperform unequal error protection, as shown in Figure

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ISBN: 978-960-6766-83-1 285 ISSN: 1790-2769

1. To satisfy the differentiated QoS, we adopt powerassignment strategies and different transmissiontechniques for different types of packets. Specifically,we provide high transmission power, long spreadingcodes with a length of 24, and strategies for providingsignificant error protection strategies for data packetsthat require a low BER. In contrast, low power, shortlength spreading codes, and less capable errorprotection strategies are used for the transmission ofaudio and video packets that can tolerate lessstringent BERs. The transmitting signal of the m-thkind bit stream in the baseband, )(tsm , is expressed as

( ) 2 ( ) ( )m m ms t Pa t b t (1)

In (1), P is the constant transmission power; , theweighting factor of the transmission power, )(tbm ,the data signal comprising a sequence of rectangularpulses of duration T; and )(tam , the MBOK codedescribed in the DS UWB standard [4] with optionallength L=24, 12, 6, 4, 2, 1. L is the length for MBOKcodes. The signal received at the input to the matchedfilter in the mobile receiver can be represented as

M

llmlml tntbtaPtr

1

)()()(2)( (2)

where n(t) is the additive white Gaussian noise(AWGN) process with two-sided power spectraldensity ( 2/0N ). It is assumed that l can be lockedto the l-th path as a reference path between thetransmitter and its corresponding receiver for them-th kind bit stream. l is the multi-path gain of thei-th path. The received signal to noise ratio (SNR) isgiven by

)}({

})]()(2{[

21

2

tnE

tbtaPESNR

M

llmlml

(3)

Thus, the power assignment mechanism can besummarized as follows:

Step 1:Based on the information at the OCPN output,evaluate the throughputs of the data, audio,and video messages for real-timetransmissions.

Step 2:Select appropriate parameters for unequalerror protection and proper modulation modesso that the requirements for real-timetransmissions in a wireless medical networkcan be fulfilled.

Step 3:Assign the original transmission powerweighting factor, , 10 , for the data,

audio, and video packets.Step 4:Measure the received signal-to-noise

interference ratio (SNR) for the data, audio,and video packets.

Step 5:For each type of packet, if the measured SNRof the received signal is larger than thethreshold SNR for the required BER, then thetransmission power weighting factor isupdated as , and Step 4 should beperformed next. Otherwise, we go to Step 6.

Step 6:Increase the transmission power weightingfactor as . If 1 , re-selectparameters for the unequal error protection aswell as the mode of modulation, and go toStep 3. If 1 , go to Step 4 and repeat theremaining steps.

The parameter depends on the variation in thechannel fading. The greater the variation in thechannel fading, the greater the value of ; the lesserthe variation in the channel fading, the smaller thevalue of . In addition, the smaller the variation,the larger is the power saving.

3 Simulation ResultsWe have carried out a simulation to demonstrate theproper functionality of the proposed DS UWBwireless telemedicine system. In the simulation, weused K=6, 3/4 convolution code with soft decoding,and L=12 MBOK codes for the transmission of audiopackets. For video packets, the K=6, 2/3 convolutioncode with soft decoding, and L=12 MBOK codeswere used. For data packets, the K=6, 1/2 convolutioncode with soft decoding and L=24 MBOK codeswere used. The system could perform channelestimation with a mean square error of 0.01.Moreover, we have assumed that the referencetransmission power is =1 and the originaltransmission power weighting factor is =1/15.There are four channel models (CMs) -CM1, CM2,CM3, and CM4- in the UWB system [13]. The targetchannel characteristics are described in the following.CM1 has a line-of-sight (LOS) signal similar to CM2,and CM3, while CM4 has a non-line-of-sight (NLOS)signal. The transmission distances are 0-4m, 0-4m,4-10m, to be defined, and the root mean square (RMS)delays are 5-ns, 8-ns, 15-ns, and 25-ns for CM1, CM2,CM3, and CM4, respectively. In Figure 2, CM2 andthe AWGN process with zero mean and variance 2

nare employed. Figure 2 shows the transmission powerweighting factors for data, audio, and video packetsas a function of 2

n , the transmission power weighting

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ISBN: 978-960-6766-83-1 286 ISSN: 1790-2769

for the data, video, and audio packets d , v and aare denoted by the symbols (), (O), and (Δ ),respectively. The target SNRs to meet the requiredQoS for data, video, and audio bit streams are 10.74dB, 12.09 dB and 16.10 dB, respectively. On thebasis of CM2 and the specified QoS requirements forthe audio, video, and data packets, Table I presentsthe transmission rates and the correspondingtransmission power for 15/1 in an unequal errorprotection DS UWB wireless telemedicine systemwith dB202 n . Table II shows the obtainabletransmission rates for various transmission powerfactors with 10/1 . From these two tables, wecan observe that the use of the dynamic powerassignment mechanism can maximize the systemtransmission rates or minimize the transmissionpower consumption as compared to an equal powerDS UWB system. The decrease in the transmissionpower for unequal power assignment strategy inTable I and II is calculated as

%100)()(

dva

ddvvaadva

RRRRRRRRR (4)

where aR , vR , and dR are the transmission rates forthe audio, video, and data packets in the proposed DSUWB wireless telemedicine system under a referencetransmission power, respectively; a , v , and d arethe transmission power weighting factors for theaudio, video, and data packets, respectively. Fromthe simulation results shown in Table I, it can beobserved that when the power weighting factors are7/15, 7/15, and 9/15 for the audio, video, and datapackets, respectively, the obtainable correspondingtransmission rates of 82-Mbps, 73-Mbps, and28-Mbps can meet the differentiated QoSrequirements of a wireless medical network. Ascompared to a DS UWB medical system with equalpower transmission, our system can result in powersaving up to 51.29% power saving for 15/1 .From Table II, we can observe that the power savingis 48.47% for 10/1 . The smaller the variation, the larger is the power saving. To furtherinvestigate the advantages of this system, we haveundertaken a simulation by using the measured data.Figure 3 shows the received ECG signals. The meansquare error of the original and the received ECGsignals is 0.0063 in a DS UWB wireless medicinesystem with power assignment. Figure 4 shows thereceived EEG signals. The mean square error of theoriginal and the received EEG signals is 0.0031 in aDS UWB wireless medicine system with powerassignment. It is suitable for use in the field of

medicine. Figure 5 shows the received and decodedG.729 audio signals in the DS UWB system with apower control mechanism. The mean square error ofthe original and the received audio signal is 0.003511.It is observed that the audio signal is very clear.Figure 6 shows the received and decoded JPEG2000medical image. The peak signal-to-noise ratio (PSNR)of the JPEG-2000 medical images is 36.31dB. Figure7 shows the received MPEG-4 CCD sensor videosignals with an average SNR value of 33.1dB. Fromthe above figures, we can observe that by usingpower assignment, not only can the system capacitycan be increased but also the required QoS can alsobe realized. From the above discussion, we canobserve that the proposed DS UWB transportarchitecture is a feasible platform for a wirelesstelemedicine system. In addition, such a system canachieve the maximum transmission rates, or theminimum transmission power consumption.

4 Conclusion

In this paper, power assignment schemes, unequalerror protection strategies, and MBOK codingtechniques are employed for medical messages withdifferent characteristics to achieve the differentiatedOoS requirements. In particular, for hightransmission rate and real-time interactiveaudio/video signals, we use short MBOK codes,schemes with relatively less capable error protectionschemes, and low transmission power. In contrast,long MBOK codes, more capable error protectionschemes, and high transmission power are providedfor medical signals that necessitate a stringent BER.The simulation results have shown that the proposedDS UWB transport architecture can achieve themaximum transmission rates or the minimumtransmission power consumption, and that it is afeasible platform for a wireless telemedicine system.

References:[1] D. Cypher, N. Chevrollier, N. Montavont, and N.

Golmie, “Preailing over Wires in HealthcareEnvironments: Benefits and Challenges,” IEEECommunications Magazine, pp.56-63, 2006, pp.56-63.

[2] C. F. Lin, J. Y. Chen, R. H. Shiu, and S. H. Chang,“A Ka Band WCDMA-based LEO TransportArchitecture in Mobile Telemedicine,” appearin Telemedicine in the 21st Century, NovaScience Publishers, Inc, USA, 2008.(invitedbook chapter)

[3] C. F. Lin, W. T. Chang, H. W. Lee, and S. I.Hung,“Downlink Power Control in Multi-Code

12th WSEAS International Conference on SYSTEMS, Heraklion, Greece, July 22-24, 2008

ISBN: 978-960-6766-83-1 287 ISSN: 1790-2769

CDMA Mobile Medicine System,” Medical &Biological Engineering & Computing, vol.44,2006, pp.437-444.

[4] C. F. Lin, and K. T. Chang,” A PowerAssignment Mechanism in Ka BandOFDM-based Multi-satellites MobileTelemedicine,” J. of Medical and BiologicalEngineering 2008, pp.17-22.

[5] C. F. Lin and C. Y. Li, “A Power Control Scheme in DS UWB Wireless medical System,“World Congress on Medical Physics andBiomedical Engineering, 2006, pp.3851~3855.

[6] C. F. Lin and C. Y. Li , “A DS UWBWirelessmedical System, “ IEEEInternational Conference on ConsumerElectronics, 2007, pp.335-336.

[7] J. E. Cabral and Y. Kim,“Multimedia Systems forTelemedicine and Their CommunicationsRequirement,” IEEE Commun. Magazine, vol.34, 1996, pp. 20-27.

[8] B. Fong, A.C.M. Fong, P.B. Rapajic, G.Y.Hong, ”Mobile Telemedicine for Accident andEmergency Scenes in Tropical Regions,” WSEAS Trans. Comm. Vol.2, 2003, pp.361-364.

[9] G. Mandellos, M. Koukias, G. Anastassopoulos,D. Lymperopoulos, “A new SCP-ECG modulefor telemedicine services,” WSEASTrans.Computer, Vol.3, 2004, pp.1258-1263.

[10] D. Kralj, and M. Stamenkovic, “Health Serviceand Environment Management System,” WSEAS International Conference onMathematical Biology and Ecology 2006,pp.20-24.

[11]FCC, “Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wideband TransmissionSystems,” First Report and Order, ET Docket98-153, FCC 02-8, adopted/released, Feb.14/Apr. 22, 2002.

[12] DS-UWB Physical Layer Submission to 802.15Task Group 3a, IEEE P802.15-04/0137r4,January, 2005.

[13] Channel Modeling Sub-committee Report Final,IEEE P802.15-02/490r1, Febubary, 2003.

[14] M. Woo, N. Prabhu, and A. Ghafoor, "Dynamicresource allocation for multimedia services inmobile communication environments, " IEEE J.Select. Areas Commun., Vol. 13, 1995, pp.913-922.

[15] 3GPP TS 25.212 v6.2.0, 3rd GenerationPartnership Project;Technical SpecificationGroup radio Access network; Multiplexing andchannel coding (FDD) , 2005.

Figure 2. Transmission power weighting factors fordata, audio, and video as a function of the AWGNwith CM2. (power weighting factors for data, video,and audio packets are represented by , O, and Δ, respectively).

Table I

Table II

Figure 3 Received ECG signal in the DS UWBsystem with unequal error protection. (MSE= 0.0063)

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ISBN: 978-960-6766-83-1 288 ISSN: 1790-2769

Figure 4 Received EEG signal in the DS UWBsystem with unequal error protection. (MSE=0.0031)

Figure 5 Received and decoded G.729 audio signalstested in the DS UWB system with unequal errorprotection. (MSE=0.003511)

Figure 6 Received image signals tested in the DSUWB wireless medical system with unequal errorprotection. (PSNR=36.31dB)

0 1 2 3 4 5 632

32.5

33

33.5

34

34.5

35

35.5

Time(s)

PS

NR

(dB)

Figure 7 Received PSNR values of MPEG-4 CCDsensor video signals tested in the DS UWBwireless medical system with unequal errorprotection.

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ISBN: 978-960-6766-83-1 289 ISSN: 1790-2769